Apparatus for the measurement of stiffness of flexible materials



Sept 22, 1931- T. DANTZIG ET AL 1,324,395

APPARATUS FOR THE MEASUREMENT OF STIFFNESS OF FLEXIBLE MATERIALS Filed Aug. 9. 192a" INXZE NT DR S jflarrzgi Patented Sept. 22, 1931 UNITED STATES PATENT OFFICE TOBIAS DAN TZIG .AND ESTHER C. PETERSON, OF WASHINGTON, DISTRICT 0! COLUMBIA, DEDICATED TO THE GOVERNMENT AND THE PEOPLE OF THE UNITED STATES OF AMERICA APPARATUS FOR THE MEASUREMENT OF STIFFNESS 0F FLEXIBLE MATERIALS Application filed August 9, 1928. Serial No. 298,577.

(GRANTED UNDER THE ACT OF MARCH 3, 1883, AS AMENDED APRIL 30, 1928 370 0. G. 757) This application is made. under the act approved April 30, 1928. and the invention herein described, if patented, may be. manufactured and used by or for the (irovernment for governnumtal purposes without payment to us of any royalty thereon.

In the accompanying drawings Fig. l is a view in elevation of the apparatus we employ in our measurements: and Fig. 2 is a vertical section of the apparatus on the line 22 of Fig. 1.

Referring to the drawings. it will he seen that B'represents a vertical boa rd. near the upper edge B of which are mounted flexible rollers 1t and R. The Board li also supports an inclined guide (t the longitudinal axis of which passes through the line of contact of the rollers R and R.

In operating the device. test material is cut into a. strip E of (OllVtlllOllt width and passed between the rollers R and R the free end F of the strip resting on the guide G. The lower roller R is then turned by means of the handle TI until the free end of the strip barely touches the guide (i. The guide is provided with a scal S the origin of which is at the line of contact 0. The stiffness numher hereinafter explained is read off the scale at the point where the free. end of the strip touches the guide.

The rubber rollers it and It are mounted on pins P. Each pin turns in two sl eve P which are mounted at one end in the vertical board B and at the other in the wall of a shelf which is fastened at one corner of the board by means of a bracket Zn. The guide G has an angle cross section, its protrading part serving as a guide. for the material.

The construction of this apparatus is hased on the following principle: Then a flexible strip is clamped at one end and freely suspended, the strip assumes a certain curved position, the. form of which depends upon the elastic modulus of the material. the thickness and width of the material and its total length from its clamped to its freeend. For a given material the. thickness and weight remain sensibly constant; the, curve, therefore, depends merely on the length of the strip and on the elastic modulus. For purposes of measurement, we define the stiffness of the material as a number proportional to the cube root of the elastic modulus.

A mathematical analysis of the problem from the standpoint of the theory of elasticity shows that the rectilinear distance between the free end and the clamped end can with excellent a-pproximationbe taken as proportional to the number defined as stiffness in the preceding paragraph. For this reason if a uniform scale of convenientunit has been marked on the board with the zero point at the point of contact of the two rollers between which the material is clamped the position of the free end of the strip would measure the stiffness as defined.

Two methods may be followed in selecting the unit. \Vecan be guided in our selection by a more or less arbitrary judgment as to what numbers would be most adaptable to the trade. We also may calihrate our scale by using standard metal foil of variable thickness. If the second method is adopted and the stiffness of a material is found to he 7, the interpretation of the reading would he that our material is as stiff as a certain metal foil .007 inches thick.

\Ve claim:

An apparatus for measuring the stiffness of flexible material, comprising means for clamping said material at one end, a downwardly inclined guide for said material at its other end, said guide having a scale provided with calibrations having their origin at the clamp end of said flexible material, and means for supporting said clamping means and said guide.

'IOBIAS DANTZIG. ESTHER C. PETERSON. 

